Defrost system and method of defrosting an evaporator section of a temperature control unit

ABSTRACT

A defrost system for a temperature control unit includes an evaporator section having a refrigerant inlet (54) and a refrigerant outlet. Also disclosed is a first heating element (80). Further disclosed is a second heating element (82), the first heating element (80) located closer to the refrigerant inlet (54) than the second heating element (82) is to the refrigerant inlet (54). Yet further disclosed is a first sensing device (60) for detecting ice buildup at the refrigerant inlet (54), wherein heating activation of the first heating element (80) is determined at least in part by ice buildup detection of the first sensing device (60). Also disclosed is a second sensing device (70) for detecting ice buildup along the second heating element (82), wherein heating activation of the second heating element (82) is determined at least in part by ice buildup detection of the second sensing device (70).

BACKGROUND

This disclosure relates generally to refrigeration systems and, more particularly, to an electric heater defrost system for such refrigeration systems.

A transport refrigeration system used to control enclosed areas, such as the insulated box used on trucks, trailers, containers, or similar intermodal units, functions by absorbing heat from the enclosed area and releasing heat outside of the box into the environment. Environmental concerns associated with certain refrigerants may lead to mandates for the use of low global warming potential (GWP) refrigerants, but there is a concern for systems that use such refrigerants because, as currently designed, low GWP refrigerants have properties during phase change that may create a temperature glide, or a change in temperature at constant pressure while in the liquid and vapor mixed phase. This creates uneven temperature distribution within evaporator coils that can cause ice buildup on the inlet side of the evaporator coil while the remainder of the evaporator coil stays above freezing temperature. This creates difficulty predicting when to defrost the ice, and ensuring that the coil is fully cleared of ice. Ice buildup undesirably reduces cooling capacity.

BRIEF SUMMARY

Disclosed is a defrost system for a temperature control unit including an evaporator section having a refrigerant inlet and a refrigerant outlet. Also disclosed is a first heating element. Further disclosed is a second heating element, the first heating element located closer to the refrigerant inlet than the second heating element is to the refrigerant inlet. Yet further disclosed is a first sensing device for detecting ice buildup at the refrigerant inlet, wherein heating activation of the first heating element is determined at least in part by ice buildup detection of the first sensing device. Also disclosed is a second sensing device for detecting ice buildup along the second heating element, wherein heating activation of the second heating element is determined at least in part by ice buildup detection of the second sensing device.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that at least one of the first sensing device and the second sensing device is an air switch for detecting a pressure differential.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the first heating element and the second heating element are each electric heating elements.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the first heating element and the second heating element are oriented perpendicular to each other.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the first heating element is oriented vertically relative to the evaporator section, the second heating element oriented along a longitudinal direction of the evaporator section.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the first heating element may be activated during cooling system operation of the temperature control unit.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the first heating element is one of a plurality of first heating elements and the second heating element is one of a plurality of second heating elements, each of the first heating elements located closer to the refrigerant inlet than each of the plurality of second heating elements is to the refrigerant inlet.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the temperature control unit is a transport refrigeration unit.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the first sensing device and the second sensing device are each temperature sensors for detecting a temperature differential.

Also disclosed is a method of defrosting an evaporator section of a temperature control unit. The method includes detecting the presence of ice buildup at a first location proximate a refrigerant inlet of the evaporator section with a first sensing device. The method also includes detecting the presence of ice buildup at a second location of the evaporator section with a second sensing device. The method further includes activating a first heating element upon detection of the presence of ice buildup at the first location. The method yet further includes activating a second heating element upon detection of the presence of ice buildup at the second location.

In addition to one or more of the features described above, or as an alternative, further embodiments may include separately controlling the first heating element and the second heating element.

In addition to one or more of the features described above, or as an alternative, further embodiments may include activating the first heating element without activating the second heating element.

In addition to one or more of the features described above, or as an alternative, further embodiments may include activating the first heating element during cooling system operation of the temperature control unit.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that detecting the presence of ice buildup at the first location and the second location comprises detecting a first pressure differential at the first location and detecting a first pressure differential at the second location.

In addition to one or more of the features described above, or as an alternative, further embodiments may include orienting the first heating element and the second heating element perpendicular to each other.

In addition to one or more of the features described above, or as an alternative, further embodiments may include orienting the first heating element vertically relative to the evaporator section, and orienting the second heating element along a longitudinal direction of the evaporator section.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is illustrated by way of example and not limited in the accompanying figures in which like reference numerals indicate similar elements.

FIG. 1 is a temperature control system in use with a transport vehicle;

FIG. 2 is a plot of temperature vs. entropy for various refrigerants within an evaporator section of the temperature control system;

FIG. 3 is a schematic illustration of the evaporation section of the temperature control system; and

FIG. 4 is a schematic illustration of heating elements within the evaporator section.

DETAILED DESCRIPTION

Disclosed herein are embodiments associated with defrosting an evaporator section of a temperature control system. Although various refrigeration systems may benefit from the embodiments disclosed herein, FIG. 1 illustrates an application of the embodiments on a transport refrigeration system 10 associated with a trailer 12 pulled by a tractor 14. The trailer 12 includes a cargo container/box 16 defining an interior space 18, wherein perishable product is stowed for transport. The transport refrigeration system 10 is operative to climate control the atmosphere within the interior space 18 of the cargo container/box 16 of the trailer 12. It is to be understood that the system and method disclosed herein may be applied not only to refrigeration systems associated with trailers, but also to refrigeration systems applied to refrigerated trucks, to intermodal containers equipped with gensets, and to other refrigeration systems including a refrigerant unit having an engine driven compressor.

Conventional refrigeration cycle components, such as a compressor, a refrigerant heat rejection heat exchanger, an expansion device, a refrigerant evaporator section, and a suction modulation valve connected in a closed loop refrigerant circuit may be included in the transport refrigeration system, but are not illustrated in FIG. 1. The transport refrigeration system 10 is mounted as in conventional practice to an exterior wall of the truck, trailer or container.

FIG. 2 illustrates a temperature glide for three different refrigerants. As shown, a HFC refrigerant 20, such as R404a or the like, is shown to have a low temperature glide, which refers to the slope of the plot of temperature vs. entropy. A HFC “lower GWP” 30 such as R452a or the like has a slightly higher temperature glide, relative to the HFC refrigerant 20. A low GWP refrigerant 40 has a high temperature glide, relative to refrigerants 20 and 30. This illustrates that the low GWP refrigerant 40 has a substantially lower temperature at the inlet of the evaporator section, when compared to the evaporator section outlet temperature. Such a glide results in ice formation at the inlet more frequently than ice formation at the outlet and intermediate locations therebetween.

Referring now to FIGS. 3 and 4, a portion of the evaporator section 50 is illustrated. The evaporator section 50 includes evaporator coils 52 for routing the low GWP refrigerant 40 throughout the evaporator section 50. The embodiments described herein include at least one electric heater element that is dedicated to ice defrosting at the inlet 54 of the evaporator section 50. This avoids the issue of incomplete defrosting at the inlet during a defrost cycle that relies on a single sensing device located away from the inlet, as well as inefficiencies associated with initiating full defrost cycles too frequently if a single sensing device was located at the inlet 54.

As shown in FIG. 3, a first sensing device 60 is located proximate the inlet 54 of the evaporator section 50. A second sensing device 70 is located further from the inlet 54 than the distance between the first sensing device 60 and the inlet 54. The sensing devices 60, 70 detect the formation of ice. In some embodiments, one or both of the sensing devices 60, 70 are air switches configured to detect a pressure drop in their respective locations. In some embodiments, one or both of the sensing devices 60, 70 are temperature sensors that detect a temperature difference between the two sensors and providing a response, such as turning on the heating elements. As shown in FIG. 3, ice 72 may be present at the inlet 54, but not along any other region of the evaporator section 50. To avoid shutting down the cooling system for a full defrost cycle, the embodiments described herein facilitate defrosting at only the inlet 54.

FIG. 4 illustrates two sets of heating elements within the evaporator section 50. Although a plurality of each type of heating element is shown, it is to be appreciated that a single heating element may be used in conjunction with each sensing device. In particular, a first heating element 80 (or first plurality of heating elements 80) is located proximate the inlet 54. The first heating element(s) 80 may be positioned in various orientations. In the illustrated embodiment, the first heating element(s) 80 are oriented substantially vertically within the evaporator section 50. The substantially vertical orientation may be advantageous to dominate the heating distribution at the inlet 54.

A second heating element 82 (or second plurality of heating elements 82) is located further from the inlet 54, when compared to the distance between the first heating element 80 and the inlet 54. The second heating element(s) 82 may be positioned in various orientations. In the illustrated embodiment, the second heating element(s) 82 are oriented substantially along a longitudinal direction of the evaporator section 50, such that the heating elements 80, 82 are arranged substantially perpendicularly to each other.

The first heating element(s) 80 are electric heaters separately controlled based on the distinct sensing device 60, 70 and with separate contactors 84. The heating elements 80, 82 radiate heat to melt ice. The first heating element(s) 80 is activated when the first sensing device 60 detects the presence of ice formation proximate the inlet 54. The second heating element(s) 82 is activated when the second sensing device 70 detects the presence of ice formation further from the inlet 54. Unlike the first heating element activation, activation of the second heating element 82 requires a full defrost cycle to be initiated.

The embodiments described herein detect when ice buildup has limited cooling capacity when the second sensing device 60 has not initiated a full defrost cycle. Heating may be provided to the inlet iced area while the remainder of the evaporator coil is continuing to reduce the box temperature and until the airflow is no longer blocked by ice in the inlet region. This reduces the number of full defrost cycles needed if the second sensing device were to be located at the initial point of icing. The embodiments control refrigerant glide effects on system performance until the entire cargo area has been dehumidified.

Embodiments may be implemented using one or more technologies. In some embodiments, an apparatus or system may include one or more processors, and memory storing instructions that, when executed by the one or more processors, cause the apparatus or system to perform one or more methodological acts as described herein. Various mechanical components known to those of skill in the art may be used in some embodiments.

Embodiments may be implemented as one or more apparatuses, systems, and/or methods. In some embodiments, instructions may be stored on one or more computer program products or computer-readable media, such as a transitory and/or non-transitory computer-readable medium. The instructions, when executed, may cause an entity (e.g., a processor, apparatus or system) to perform one or more methodological acts as described herein.

While the disclosure has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the disclosure is not limited to such disclosed embodiments. Rather, the disclosure can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the scope of the disclosure. Additionally, while various embodiments have been described, it is to be understood that aspects of the disclosure may include only some of the described embodiments. Accordingly, the disclosure is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims. 

What is claimed is:
 1. A defrost system for a temperature control unit comprising: an evaporator section having a refrigerant inlet and a refrigerant outlet; a first heating element; a second heating element, the first heating element located closer to the refrigerant inlet than the second heating element is to the refrigerant inlet; a first sensing device for detecting ice buildup at the refrigerant inlet, wherein heating activation of the first heating element is determined at least in part by ice buildup detection of the first sensing device; and a second sensing device for detecting ice buildup along the second heating element, wherein heating activation of the second heating element is determined at least in part by ice buildup detection of the second sensing device.
 2. The defrost system of claim 1, wherein at least one of the first sensing device and the second sensing device is an air switch for detecting a pressure differential.
 3. The defrost system of claim 1, wherein the first heating element and the second heating element are each electric heating elements.
 4. The defrost system of claim 1, wherein the first heating element and the second heating element are oriented perpendicular to each other.
 5. The defrost system of claim 1, wherein the first heating element is oriented vertically relative to the evaporator section, the second heating element oriented along a longitudinal direction of the evaporator section.
 6. The defrost system of claim 1, wherein the first heating element may be activated during cooling system operation of the temperature control unit.
 7. The defrost system of claim 1, wherein the first heating element is one of a plurality of first heating elements and the second heating element is one of a plurality of second heating elements, each of the first heating elements located closer to the refrigerant inlet than each of the plurality of second heating elements is to the refrigerant inlet.
 8. The defrost system of claim 1, wherein the temperature control unit is a transport refrigeration unit.
 9. The defrost system of claim 1, wherein the first sensing device and the second sensing device are each temperature sensors for detecting a temperature differential.
 10. A method of defrosting an evaporator section of a temperature control unit comprising: detecting the presence of ice buildup at a first location proximate a refrigerant inlet of the evaporator section with a first sensing device; detecting the presence of ice buildup at a second location of the evaporator section with a second sensing device; activating a first heating element upon detection of the presence of ice buildup at the first location; and activating a second heating element upon detection of the presence of ice buildup at the second location.
 11. The method of claim 10, further comprising separately controlling the first heating element and the second heating element.
 12. The method of claim 10, further comprising activating the first heating element without activating the second heating element.
 13. The method of claim 12, further comprising activating the first heating element during cooling system operation of the temperature control unit.
 14. The method of claim 10, wherein detecting the presence of ice buildup at the first location and the second location comprises detecting a first pressure differential at the first location and detecting a first pressure differential at the second location.
 15. The method of claim 10, further comprising orienting the first heating element and the second heating element perpendicular to each other.
 16. The method of claim 10, further comprising orienting the first heating element vertically relative to the evaporator section, and orienting the second heating element along a longitudinal direction of the evaporator section. 